In adding another to the large number of books which treat upon Mechanics, and especially of that class devoted to what is called Mechanical Engineering, it will be proper to explain some of the reasons for preparing the present work; and as these explanations will constitute a part of the work itself, and be directed to a subject of some interest to a learner, they are included in the Introduction.
First I will notice that among our many books upon mechanical subjects there are none that seem to be directed to the instruction of apprentice engineers; at least, there are none directed to that part of a mechanical education most difficult to acquire, a power of analysing and deducing conclusions from commonplace matters.
Our text-books, such as are available for apprentices, consist mainly of mathematical formul? relating to forces, the properties of material, examples of practice, and so on, but do not deal with the operation of machines nor with constructive manipulation, leaving out that most important part of a mechanical education, which consists in special as distinguished from general knowledge.
The theorems, formul?, constants, tables, and rules, which are generally termed the principles of mechanics, are in a sense only symbols of principles; and it is possible, as many facts will prove, for a learner to master the theories and symbols of mechanical principles, and yet not be able to turn such knowledge to practical account.
A principle in mechanics may be known, and even familiar to a learner, without being logically understood; it might even be said that both theory and practice may be learned without the power to connect and apply the two things. A person may, for example, understand the geometry of tooth gearing and how to lay out teeth of the proper form for various kinds of wheels, how to proportion and arrange the spokes, rims, hubs, and so on; he may also understand the practical application of wheels as a means of varying or transmitting motion, but between this knowledge and a complete wheel lies a long train of intricate processes, such as pattern-making, moulding, casting, boring, and fitting. Farther on comes other conditions connected with the operation of wheels, such as adaptation, wear, noise, accidental strains, with many other things equally as important, as epicycloidal curves or other geometrical problems relating to wheels.
Text-books, such as relate to construction, consist generally of examples, drawings, and explanations of machines, gearing, tools, and so on; such examples are of use to a learner, no doubt, but in most cases he can examine the machines themselves, and on entering a shop is brought at once in contact not only with the machines but also with their operation. Examples and drawings relate to how machines are constructed, but when a learner comes to the actual operation of machines, a new and more interesting problem is reached in the reasons why they are so constructed.
The difference between how machinery is constructed and why it is so constructed, is a wide one. This difference the reader should keep in mind, because it is to the second query that the present work will be mainly addressed. There will be an attempt—an imperfect one, no doubt, in some cases—to deduce from practice the causes which have led to certain forms of machines, and to the ordinary processes of workshop manipulation. In the mind of a learner, whether apprentice or student, the strongest tendency is to investigate why certain proportions and arrangement are right and others wrong—why the operations of a workshop are conducted in one manner instead of another? This is the natural habit of thought, and the natural course of inquiry and investigation is deductive.
Nothing can be more unreasonable than to expect an apprentice engineer to begin by an inductive course in learning and reasoning about mechanics. Even if the mind were capable of such a course, which can not be assumed in so intricate and extensive a subject as mechanics, there would be a want of interest and an absence of apparent purpose which would hinder or prevent progress. Any rational view of the matter, together with as many facts as can be cited, will all point to the conclusion that apprentices must learn deductively, and that some practice should accompany or precede theoretical studies. How dull and objectless it seems to a young man when he toils through "the sum of the squares of the base and perpendicular of a right-angle triangle," without knowing a purpose to which this problem is to be applied; he generally wonders why such puzzling theorems were ever invented, and what they can have to do with the practical affairs of life. But if the same learner were to happen upon a builder squaring a foundation by means of the rule "six, eight, and ten," and should in this operation detect the application of that tiresome problem of "the sum of the squares," he would at once awake to a new interest in the matter; what was before tedious and without object, would now appear useful and interesting. The subject would become fascinating, and the learner would go on with a new zeal to trace out the connection between practice and other problems of the kind. Nothing inspires a learner so much as contact with practice; the natural tendency, as before said, is to proceed deductively.
A few years ago, or even at the present time, many school-books in use which treat of mechanics in connection with natural philosophy are so arranged as to hinder a learner from grasping a true conception of force, power, and motion; these elements were confounded with various agents of transmission, such as wheels, wedges, levers, screws, and so on. A learner was taught to call these things "mechanical powers," whatever that may mean, and to compute their power as mechanical elements. In this manner was fixed in the mind, as many can bear witness, an erroneous conception of the relations between power and the means for its transmission; the two things were confounded together, so that years, and often a lifetime, has not served to get rid of the idea of power and mechanism being the same. To such teaching can be traced nearly all the crude ideas of mechanics so often met with among those well informed in other matters. In the great change from empirical rules to proved constants, from special and experimental knowledge to the application of science in the mechanic arts, we may, however, go too far. The incentives to substitute general for special knowledge are so many, that it may lead us to forget or underrate that part which cannot come within general rules.
The labour, dirt, and self-denial inseparable from the acquirement of special knowledge in the mechanic arts are strong reasons for augmenting the importance and completeness of theoretical knowledge, and while it should be, as it is, the constant object to bring everything, even manipulative processes, so far as possible, within general rules, it must not be forgotten that there is a limit in this direction.
In England and America the evils which arise from a false or over estimate of mere theoretical knowledge have thus far been avoided. Our workshops are yet, and must long remain, our technological schools. The money value of bare theoretical training is so fast declining that we may be said to have passed the point of reaction, and that the importance of sound practical knowledge is beginning to be more felt than it was some years ago. It is only in those countries where actual manufactures and other practical tests are wanting, that any serious mistake can be made as to what should constitute an education in mechanics. Our workshops, if other means fail, will fix such a standard; and it is encouraging to find here and there among the outcry for technical training, a note of warning as to the means to be employed.
During the meeting of the British Association in Belfast (1874), the committee appointed to investigate the means of teaching Physical Science, reported that "the most serious obstacle discovered was an absence from the minds of the pupils of a firm and clear grasp of the concrete facts forming a base of the reasoning processes they are called upon to study; and that the use of text-books should be made subordinate to an attendance upon lectures and demonstrations."
Here, in reference to teaching science, and by an authority which should command our highest confidence, we have a clear exposition of the conditions which surround mechanical training, with, however, this difference, that in the latter "demonstration" has its greatest importance.
Professor John Sweet of Cornell University, in America, while delivering an address to the mechanical engineering classes, during the same year, made use of the following words: "It is not what you 'know' that you will be paid for; it is what you can 'perform,' that must measure the value of what you learn here." These few words contain a truth which deserves to be earnestly considered by every student engineer or apprentice; as a maxim it will come forth and apply to nearly everything in subsequent practice.
I now come to speak directly of the present work and its objects. It may be claimed that a book can go no further in treating of mechanical manipulation than principles or rules will reach, and that books must of necessity be confined to what may be called generalities. This is in a sense true, and it is, indeed, a most difficult matter to treat of machine operations and shop processes; but the reason is that machine operations and shop processes have not been reduced to principles or treated in the same way as strains, proportions, the properties of material, and so on. I do not claim that manipulative processes can be so generalised—this would be impossible; yet much can be done, and many things regarded as matters of special knowledge can be presented in a way to come within principles, and thus rendered capable of logical investigation.
Writers on mechanical subjects, as a rule, have only theoretical knowledge, and consequently seldom deal with workshop processes. Practical engineers who have passed through a successful experience and gained that knowledge which is most difficult for apprentices to acquire, have generally neither inclination nor incentives to write books. The changes in manipulation are so frequent, and the operations so diversified, that practical men have a dread of the criticisms which such changes and the differences of opinion may bring forth; to this may be added, that to become a practical mechanical engineer consumes too great a share of one's life to leave time for other qualifications required in preparing books. For these reasons "manipulation" has been neglected, and for the same reasons must be imperfectly treated here. The purpose is not so much to instruct in shop processes as to point out how they can be best learned, the reader for the most part exercising his own judgment and reasoning powers. It will be attempted to point out how each simple operation is governed by some general principle, and how from such operations, by tracing out the principle which lies at the bottom, it is possible to deduce logical conclusions as to what is right or wrong, expedient or inexpedient. In this way, it is thought, can be established a closer connection between theory and practice, and a learner be brought to realise that he has only his reasoning powers to rely on; that formul?, rules, tables, and even books, are only aids to this reasoning power, which alone can master and combine the symbol and the substance.
No computations, drawings, or demonstrations of any kind will be employed to relieve the mind of the reader from the care of remembering and a dependence on his own exertions. Drawings, constants, formul?, tables, rules, with all that pertains to computation in mechanics, are already furnished in many excellent books, which leave nothing to be added, and such books can be studied at the same time with what is presented here.
The book has been prepared with a full knowledge of the fact, that what an apprentice may learn, as well as the time that is consumed in learning, are both measured by the personal interest felt in the subject studied, and that such a personal interest on the part of an apprentice is essential to permanent success as an engineer. A general dryness and want of interest must in this, as in all cases, be a characteristic of any writing devoted to mechanical subjects: some of the sections will be open to this charge, no doubt, especially in the first part of the book; but it is trusted that the good sense of the reader will prevent him from passing hurriedly over the first part, to see what is said, at the end, of casting, forging, and fitting, and will cause him to read it as it comes, which will in the end be best for the reader, and certainly but fair to the writer.
By examining the subject of applied mechanics and shop manipulation, a learner may see that the knowledge to be acquired by apprentices can be divided into two departments, that may be called general and special. General knowledge relating to tools, processes and operations, so far as their construction and action may be understood from general principles, and without special or experimental instruction. Special knowledge is that which is based upon experiment, and can only be acquired by special, as distinguished from general sources.
To make this plainer, the laws of forces, the proportion of parts, strength of material, and so on, are subjects of general knowledge that may be acquired from books, and understood without the aid of an acquaintance with the technical conditions of either the mode of constructing or the manner of operating machines; but how to construct proper patterns for castings, or how the parts of machinery should be moulded, forged, or fitted, is special knowledge, and must have reference to particular cases. The proportions of pulleys, bearings, screws, or other regular details of machinery, may be learned from general rules and principles, but the hand skill that enters into the manufacture of these articles cannot be learned except by observation and experience. The general design, or the disposition of metal in machine-framing, can be to a great extent founded upon rules and constants that have general application; but, as in the case of wheels, the plans of moulding such machine frames are not governed by constant rules or performed in a uniform manner. Patterns of different kinds may be employed; moulds may be made in various ways, and at a greater and less expense; the metal can be mixed to produce a hard or a soft casting, a strong or a weak one; the conditions under which the metal is poured may govern the soundness or shrinkage,—things that are determined by special instead of general conditions.
The importance of a beginner learning to divide what he has to learn into these two departments of special and general, has the advantage of giving system to his plans, and pointing out that part of his education which must be acquired in the workshop and by practical experience. The time and opportunities which might be devoted to learning the technical manipulations of a foundry, for instance, would be improperly spent if devoted to metallurgic chemistry, because the latter may be studied apart from practical foundry manipulation, and without the opportunity of observing casting operations.
It may also be remarked that the special knowledge involved in applied mechanics is mainly to be gathered and retained by personal observation and memory, and that this part is the greater one; all the formul? relating to machine construction may be learned in a shorter time than is required to master and understand the operations which may be performed on an engine lathe. Hence first lessons, learned when the mind is interested and active, should as far as possible include whatever is special; in short, no opportunity of learning special manipulation should be lost. If a wheel pattern come under notice, examine the manure in which it is framed together, the amount of draught, and how it is moulded, as well as to determine whether the teeth have true cycloidal curves.
Once, nearly all mechanical knowledge was of the class termed special, and shop manipulations were governed by empirical rules and the arbitrary opinions of the skilled; an apprentice entered a shop to learn a number of mysterious operations, which could not be defined upon principles, and only understood by special practice and experiment. The arrangement and proportions of mechanism were also determined by the opinions of the skilled, and like the manipulation of the shop, were often hid from the apprentice, and what he carried in his memory at the end of an apprenticeship was all that he had gained. The tendency of this was to elevate those who were the fortunate possessors of a strong natural capacity, and to depress the position of those less fortunate in the matter of mechanical "genius," as it was called. The ability to prepare proper designs, and to succeed in original plans, was attributed to a kind of intuitive faculty of the mind; in short, the mechanic arts were fifty years ago surrounded by a superstition of a different nature, but in its influences the same as superstition in other branches of knowledge.
But now all is changed: natural phenomena have been explained as being but the operation of regular laws; so has mechanical manipulation been explained as consisting in the application of general principles, not yet fully understood, but far enough, so that the apprentice may with a substantial education, good reasoning powers, and determined effort, force his way where once it had to be begged. The amount of special knowledge in mechanical manipulation, that which is irregular and modified by special conditions, is continually growing less as generalisation and improvement go on.
Another matter to be considered is that the engineering apprentice, in estimating what he will have to learn, must not lose sight of the fact that what qualifies an engineer of to-day will fall far short of the standard that another generation will fix, and of that period in which his practice will fall. This I mention because it will have much to do with the conceptions that a learner will form of what he sees around him. To anticipate improvement and change is not only the highest power to which a mechanical engineer can hope to attain, but is the key to his success.
By examining the history of great achievements in the mechanic arts, it will be seen that success has been mainly dependent upon predicting future wants, as well as upon an ability to supply such wants, and that the commercial value of mechanical improvements is often measured by conditions that the improvements themselves anticipate. The invention of machine-made drills, for example, was but a small matter; but the demand that has grown up since, and because of their existence, has rendered this improvement one of great value. Moulded bearings for shafts were also a trifling improvement when first made, but it has since influenced machine construction in America in a way that has given great importance to the invention.
It is generally useless and injudicious to either expect or to search after radical changes or sweeping improvements in machine manufacture or machine application, but it is important in learning how to construct and apply machinery, that the means of foreseeing what is to come in future should at the same time be considered. The attention of a learner can, for example, be directed to the division of labour, improvements in shop system, how and where commercial interests are influenced by machinery, what countries are likely to develop manufactures, the influence of steam-hammers on forging, the more extended use of steel when cheapened by improved processes for producing it, the division of mechanical industry into special branches, what kind of machinery may become staple, such as shafts, pulleys, wheels, and so on. These things are mentioned at random, to indicate what is meant by looking into the future as well as at the present.
Following this subject of future improvement farther, it may be assumed that an engineer who understands the application and operation of some special machine, the principles that govern its movements, the endurance of the wearing surfaces, the direction and measure of the strains, and who also understands the principles of the distribution of material, arrangement, and proportions,—that such an engineer will be able to construct machines, the plans of which will not be materially departed from so long as the nature of the operations to which the machines are applied remain the same.
A proof of this proposition is furnished in the case of standard machine tools for metal-cutting, a class of machinery that for many years past has received the most thorough attention at the hands of our best mechanical engineers.
Standard tools for turning, drilling, planing, boring, and so on, have been changed but little during twenty years past, and are likely to remain quite the same in future. A lathe or a planing-machine made by a first-class establishment twenty years ago has, in many cases, the same capacity, and is worth nearly as much in value at the present time as machine tools of modern construction—a test that more than any other determines their comparative efficiency and the true value of the improvements that have been made. The plans of the framing for machine tools have been altered, and many improvements in details have been added; yet, upon the whole, it is safe to assume, as before said, that standard tools for metal-cutting have reached a state of improvement that precludes any radical changes in future, so long as the operations in metal-cutting remain the same.
This state of improvement which has been reached in machine-tool manufacture, is not only the result of the skill expended on such tools, but because as a notable exception they are the agents of their own production; that is, machine tools produce machine tools, and a maker should certainly become skilled in the construction of implements which he employs continually in his own business. This peculiarity of machine-tool manufactures is often overlooked by engineers, and unfair comparisons made between machines of this class and those directed to wood conversion and other manufacturing processes, which machinists, as a rule, do not understand.
Noting the causes and conditions which have led to this perfection in machine-tool manufacture, and how far they apply in the case of other classes of machinery, will in a measure indicate the probable improvements and changes that the future will produce.
The functions and adaptations of machinery constitute, as already explained, the science of mechanical engineering. The functions of a machine are a foundation on which its plans are based; hence machine functions and machine effect are matters to which the attention of an apprentice should first be directed.
In the class of mechanical knowledge that has been defined as general, construction comes in the third place: first, machine functions; next, plans or adaptation of machines; and third, the manner of constructing machines. This should be the order of study pursued in learning mechanical manipulation. Instead of studying how drilling-machines, planing-machines or lathes are arranged, and next plans of constructing them, and then the principles of their operation, which is the usual course, the learner should reverse the order, studying, first, drilling, planing, and turning as operations; next, the adaptation of tools for the purposes; and third, plans of constructing such tools.
Applied to steam-engines, the same rule holds good. Steam, as a motive agent, should first be studied, then the operation of steam machinery, and finally the construction of steam-engines. This is a rule that may not apply in all cases, but the exceptions are few.
To follow the same chain of reasoning still farther, and to show what may be gained by method and system in learning mechanics, it may be assumed that machine functions consist in the application of power, and therefore power should be first studied; of this there can be but one opinion. The learner who sets out to master even the elementary principles of mechanics without first having formed a true conception of power as an element, is in a measure wasting his time and squandering his efforts.
Any truth in mechanics, even the action of the "mechanical powers" before alluded to, is received with an air of mystery, unless the nature of power is first understood. Practical demonstration a hundred times repeated does not create a conviction of truth in mechanical propositions, unless the principles of operation are understood.
An apprentice may learn that power is not increased or diminished by being transmitted through a train of wheels which change both speed and force, and he may believe the proposition without having a "conviction" of its truth. He must first learn to regard power as a constant and indestructible element—something that may be weighed, measured, and transmitted, but not created or destroyed by mechanism; then the nature of the mechanism may be understood, but not before.
To obtain a true understanding of the nature of power is by no means the difficulty for a beginner that is generally supposed ; and when once reached, the truth will break upon the mind like a sudden discovery, and ever afterwards be associated with mechanism and motion whenever seen. The learner will afterwards find himself analysing the flow of water, the traffic in the streets, the movement of ships and trains; even the act of walking will become a manifestation of power, all clear and intelligible, without that air of mystery that is otherwise inseparable from the phenomena of motion. If the learner will go on farther, and study the connection between heat and force, the mechanical equivalent of heat when developed into force and motion, and the reconversion of power into heat, he will have commenced at the base of what must constitute a thorough knowledge of mechanics, without which he will have to continually proceed under difficulties.
I am well aware of the popular opinion that such subjects are too abstruse to be understood by practical mechanics—an assumption that is founded mainly in the fact that the subject of heat and motion are not generally studied, and have been too recently demonstrated in a scientific way to command confidence and attention; but the subject is really no more difficult to understand in an elementary sense than that of the relation between movement and force illustrated in the "mechanical powers" of school-books, which no apprentice ever did or ever will understand, except by first studying the principles of force and motion, independent of mechanical agents, such as screws, levers, wedges, and so on.
It is to be regretted that there have not been books especially prepared to instruct mechanical students in the relations between heat, force, motion, and practical mechanism. The subject is, of course, treated at great length in modern scientific works, but is not connected with the operations of machinery in a way to be easily understood by beginners. A treatise on the subject, called "The Correlation and Conservation of Forces," published by D. Appleton & Co. of New York, is perhaps as good a book on the subject as can at this time be referred to. The work contains papers contributed by Professors Carpenter, Grove, Helmholtz, Faraday, and others, and has the advantage of arrangement in short sections, that compass the subject without making it tedious.
In respect to books and reading, the apprentice should supply himself with references. A single book, and the best one that can be obtained on each of the different branches of engineering, is enough to begin with. A pocket-book for reference, such as Molesworth's or Nystrom's, is of use, and should always be at hand. For general reading, nothing compares with the scientific and technical journals, which are now so replete with all kinds of information. Beside noting the present progress of engineering industry in all parts of the world, they contain nearly all besides that a learner will require.
It will be found that information of improvements and mechanical progress that a learner may gather from serial publications can always be exchanged for special knowledge in his intercourse with skilled workmen, who have not the opportunity or means of reading for themselves; and what an apprentice may read and learn in an hour can often be "exchanged" for experimental knowledge that has cost years to acquire.
(1.) Into what two divisions can a knowledge of constructive mechanics be divided?—(2.) Give an example of your own to distinguish between special and general knowledge.—(3.) In what manner is special knowledge mostly acquired?—(4.) What has been the effect of scientific investigations upon special knowledge?—(5.) What is meant by the division of labour?—(6.) Why have engineering tools been less changed than most other kinds of machinery during twenty years past?—(7.) What is meant by machine functions; adaptation; construction?—(8.) Why has the name "mechanical powers" been applied to screws, levers, wedges, and so on?—(9.) Can power be conceived of as an element or principle, independent of mechanism?
This work, as already explained, is to be devoted to mechanical engineering, and in view of the difference of opinion that exists as to what mechanical engineering comprehends, and the different sense in which the term is applied, it will be proper to explain what is meant by it here.
I am not aware that any one has defined what constitutes civil engineering, or mechanical engineering, as distinguished one from the other, nor is it assumed to fix any standard here farther than to serve the purpose of explaining the sense in which the terms will be used; yet there seems to be a clear line of distinction, which, if it does not agree with popular use of the terms, at least seems to be furnished by the nature of the business itself. It will therefore be assumed that mechanical engineering relates to dynamic forces and works that involve machine motion, and comprehends the conditions of machine action, such as torsional, centrifugal, intermittent, and irregular strains in machinery, arising out of motion; the endurance of wearing surfaces, the constructive processes of machine-making and machine effect in the conversion of material—in short, agents for converting, transmitting, and applying power.
Civil engineering, when spoken of, will be assumed as referring to works that do not involve machine motion, nor the use of power, but deal with static forces, the strength, nature, and disposition of material under constant strains, or under measured strains, the durability and resistance of material, the construction of bridges, factories, roads, docks, canals, dams, and so on; also, levelling and surveying. This corresponds to the most common use of the term civil engineering in America, but differs greatly from its application in Europe, where civil engineering is understood as including machine construction, and where the term engineering is applied to ordinary manufacturing processes.
Civil engineering, in the meaning assumed for the term, has become almost a pure mathematical science. Constants are proved and established for nearly every computation; the strength and durability of materials, from long and repeated tests, has come to be well understood; and as in the case of machine tools, the uniformity of practice among civil engineers, and the perfection of their works, attest how far civil engineering has become a true science, and proves that the principles involved in the construction of permanent works are well understood.
To estimate how much is yet to be learned in mechanical engineering, we have only to apply the same test, and when we contrast the great variance between the designs of machines and the diversity of their operation, even when applied to similar purposes, their imperfection is at once apparent. It must, however, be considered that if the rules of construction were uniform, and the principles of machine operation as well understood as the strength and arrangement of material in permanent structures, still there would remain the difficulty of adaptation to new processes, which are continually being developed.
If the steam-engine, for instance, had forty years ago been brought to such a state of improvement as to be constructed with standard proportions and arrangement for stationary purposes, all the rules, constants, and data of whatever kind that had been collected and proved, would have been but of little use in adapting steam-engines to railways and the purposes of navigation.
Mechanical engineering has by the force of circumstances been divided up into branches relating to engineering tools, railway machinery, marine engines, and so on; either branch of which constitutes a profession within itself. Most thorough study will be required to master general principles, and then a further effort to acquire proficiency in some special branch, without which there is but little chance of success at the present day.
To master the various details of machine manufacture, including draughting, founding, forging, and fitting, is of itself a work equal to most professional pursuits, to say nothing of manual skill; and when we come to add machine functions and their application, generating and transmitting power, with other things that will necessarily be included in practice, the task assumes proportions that makes it appear a hopeless one. Besides, the work of keeping progress with the mechanic arts calls for a continual accretion of knowledge; and it is no small labour to keep informed of the continual changes and improvements that are going on in all parts of the world, which may at any time modify and change both machines and processes. But few men, even under the most favourable conditions, have been able to qualify themselves as competent mechanical engineers sooner than at forty years of age.
One of the earliest cares of an apprentice should be to divest his mind of what I will call the romance of mechanical engineering, almost inseparable from such views as are often acquired in technological schools. He must remember that it is not a science he is studying, and that mathematics deal only with one branch of what is to be learned. Special knowledge, or what does not come within the scope of general principles, must be gained in a most practical way, at the expense of hard work, bruised fingers, and a disregard of much that the world calls gentility.
Looking ahead into the future, the apprentice can see a field for the mechanical engineer widening on every side. As the construction of permanent works becomes more settled and uniform, the application of power becomes more diversified, and develops problems of greater intricacy. No sooner has some great improvement, like railway and steam navigation, settled into system and regularity than new enterprises begin. To offset the undertaking of so great a work as the study of mechanical engineering, there is the very important advantage of the exclusiveness of the calling—a condition that arises out of its difficulties. If there is a great deal to learn, there is also much to be gained in learning it. It is seldom, indeed, that an efficient mechanical engineer fails to command a place of trust and honour, or to accumulate a competency by means of his calling.
If a civil engineer is wanted to survey railways, construct docks, bridges, buildings, or permanent works of any kind, there are scores of men ready for the place, and qualified to discharge the duties; but if an engineer is wanted to design and construct machinery, such a person is not easy to be found, and if found, there remains that important question of competency; for the work is not like that of constructing permanent works, where several men may and will perform the undertaking very much in the same manner, and perhaps equally well. In the construction of machinery it is different; the success will be directly as the capacity of the engineer, who will have but few precedents, and still fewer principles, to guide him, and generally has to set out by relying mainly upon his special knowledge of the operation and application of such machines as he has to construct.
(1.) How may mechanical be distinguished from civil engineering?—(2.) What test can be applied to determine the progress made in any branch of engineering?—(3.) What are some of the conditions which prevent the use of constants in machine construction?—(4.) Is mechanical engineering likely to become more exact and scientific?—(5.) Name some of the principal branches of mechanical engineering.—(6.) Which is the most extensive and important?
It may in the abstract be claimed that the dignity of any pursuit is or should be as the amount of good it confers, and the influence it exerts for the improvement of mankind. The social rank of those engaged in the various avocations of life has, in different countries and in different ages, been defined by various standards. Physical strength and courage, hereditary privilege, and other things that once recommended men for preferment, have in most countries passed away or are regarded as matters of but little importance, and the whole civilised world have agreed upon one common standard, that knowledge and its proper use shall be the highest and most honourable attainment to which people may aspire.
It may be useless or even wrong to institute invidious comparisons between different callings which are all useful and necessary, and the matter is not introduced here with any view of exalting the engineering profession; it is for some reasons regretted that the subject is alluded to at all, but there is too much to be gained by an apprentice having a pride and love for his calling to pass over the matter of its dignity as a pursuit without calling attention to it. The gauntlet has been thrown down and comparison provoked by the unfair and unreasonable place that the politician, the metaphysician, and the moral philosopher have in the past assigned to the sciences and constructive arts. Poetry, metaphysics, mythology, war, and superstition have in their time engrossed the literature of the world, and formed the subject of what was alone considered education.
In a half century past all has changed; the application of the sciences, the utilisation of natural forces, manufacturing, the transportation of material, the preparation and diffusion of printed matter, and other great matters of human interest, have come to shape our laws, control commerce, establish new relations between people and countries—in short, has revolutionised the world. So rapid has been this change that it has outrun the powers of conception, and people waken as from a dream to find themselves governed by a new master.
Considering material progress as consisting primarily in the demonstration of scientific truths, and secondly, in their application to useful purposes, we can see the position of the engineer as an agent in this great work of reconstruction now going on around us. The position is a proud one, but not to be attained except at the expense of great effort, and a denial of everything that may interfere with the acquirement of knowledge during apprenticeship and the study which must follow.
The mechanical engineer deals mainly with the natural forces, and their application to the conversion of material and transport. His calling involves arduous duties; he is brought in contact with what is rough and repulsive, as well as what is scientific and refined. He must include grease, dirt, manual labour, undesirable associations, and danger with apprenticeship, or else be content to remain without thoroughly understanding his profession.
(1.) What should determine the social rank of industrial callings?—(2.) Why have the physical sciences and mechanic arts achieved so honourable a position?—(3.) How may the general object of the engineering arts be described?—(4.) What is the difference between science and art as the terms are generally employed in connection with practical industry?
Were it not that moral influences in learning mechanics, as in all other kinds of education, lie at the bottom of the whole matter, the subject of this chapter would not have been introduced. But it is the purpose, so far as possible, to notice everything that concerns an apprentice and learner, and especially what he has to deal with at the outset; hence some remarks upon the nature of apprentice engagements will not be out of place. To acquire information or knowledge of any kind successfully and permanently, it must be a work of free volition, as well as from a sense of duty or expediency; and whatever tends to create love and respect for a pursuit or calling, becomes one of the strongest incentives for its acquirement, and the interest taken by an apprentice in his business is for this reason greatly influenced by the opinions that he may hold concerning the nature of his engagement.
The subject of apprentice engagements seems in the abstract to be only a commercial one, partaking of the nature of ordinary contracts, and, no doubt, can be so construed so far as being an exchange of "considerations," but no farther. Its intricacy is established by the fact that all countries where skilled labour exists have attempted legislation to regulate apprenticeship, and to define the terms and conditions between master and apprentice; but, aside from preventing the abuse of powers delegated to masters, and in some cases forcing a nominal fulfilment of conditions defined in contracts, such legislation, like that intended to control commerce and trade, or the opinions of men, has failed to attain the objects for which it was intended.
This failure of laws to regulate apprenticeship, which facts fully warrant us in assuming, is due in a large degree to the impossibility of applying general rules to special cases; it may be attributed to the same reasons which make it useless to fix values or the conditions of exchange by legislation. What is required is that the master, the apprentice, and the public should understand the true relations between them—the value of what is given and what is received on both sides. When this is understood, the whole matter will regulate itself without any interference on the part of the law.
The subject is an intricate one, and has been so much affected by the influence of machine improvement, and a corresponding decrease in what may be called special knowledge, that rules and propositions which would fifty years ago apply to the conditions of apprenticeship, will at the present day be wrong and unjust. Viewed in a commercial sense, as an exchange of considerations or values, apprenticeship can be regarded like other engagements; yet, what an apprentice gives as well as what he receives are alike too conditional and indefinite to be estimated by ordinary standards. An apprentice exchanges unskilled or inferior labour for technical knowledge, or for the privilege and means of acquiring such knowledge. The master is presumed to impart a kind of special knowledge, collected by him at great expense and pains, in return for the gain derived from the unskilled labour of the learner. This special knowledge given by the master may be imparted in a longer or shorter time; it may be thorough and valuable, or not thorough, and almost useless. The privileges of a shop may be such as to offset a large amount of valuable labour on the part of the apprentice, or these privileges may be of such a character as to be of but little value, and teach inferior plans of performing work.
On the other hand, the amount that an apprentice may earn by his labour is governed by his natural capacity, and by the interest he may feel in advancing; also from the view he may take of the equity of his engagement, and the estimate that he places upon the privileges and instruction that he receives. In many branches of business, where the nature of the operations carried on are measurably uniform, and have not for a long time been much affected by changes and improvements, the conditions of apprenticeship are more easy to define; but mechanical engineering is the reverse of this, it lacks uniformity both as to practice and what is produced. To estimate the actual value of apprentice labour in an engineering-work is not only a very difficult matter, but to some extent impracticable even by those of long experience and skilled in such investigations; and it is not to be expected that a beginner will under such circumstances be able to understand the value of such labour: he is generally led to the conclusion that he is unfairly treated, that his services are not sufficiently paid for, and that he is not advanced rapidly enough.
With these conclusions in his mind, but little progress will be made, and hence the reason for introducing the subject here.
The commercial value of professional or technical knowledge is generally as the amount of time, effort, and unpaid labour that has been devoted to its acquirement. This value is sometimes modified by the exclusiveness of some branch that has been made the object of special study. Exclusiveness is, however, becoming exceptional, as the secrets of manufacture and special knowledge are supplanted by the application of general principles; it is a kind of artificial protection thrown around certain branches of industry, and must soon disappear, as unjust to the public and unnecessary to success.
In business arrangements, technical knowledge and professional experience become capital, and offset money or property, not under any general rule, nor even as a consideration of which the law can define the value or prescribe conditions for. The estimate placed upon technical knowledge when rated as capital in the organisation of business firms, and wherever it becomes necessary to give such knowledge a commercial value, furnishes the best and almost the only source from which an apprentice can form an opinion of the money value of what he is to acquire during his apprenticeship.
An apprentice at first generally forms an exaggerated estimate of what he has to learn; it presents to his mind not only a great undertaking, but a kind of mystery, which he fears that he may not be able to master. The next stage is when he has made some progress, and begins to underrate the task before him, and imagine that the main difficulties are past, that he has already mastered all the leading principles of mechanics, which is, after all, but a "small matter." In a third stage an apprentice experiences a return of his first impressions as to the difficulties of his undertaking; he begins to see his calling as one that must involve endless detail, comprehending things which can only be studied in connection with personal experience; he sees "the horizon widen as it recedes," that he has hardly begun the task, instead of having completed it—even despairs of its final accomplishment.
In the workshop, mechanical knowledge of some kind is continually and often insensibly acquired by a learner, who observes the operations that are going on around him; he is continually availing himself of the experience of those more advanced, and learns by association the rules and customs of the shop, of the business, and of discipline and management. He gathers the technical terms of the fitting-shop, the forge and foundry; notes the operations of planing, turning, drilling, and boring, with the names and application of the machines directed to these operations. He sees the various plans of lifting and moving material, the arrangement and relation of the several departments to facilitate the course of the work in process; he also learns where the product of the works is sold, discusses the merits and adaptation of what is constructed, which leads to considering the wants that create a demand for this product, and the extent and nature of the market in which it is sold.
All these things constitute technical knowledge, and the privilege of their acquirement is an element of value. The common view taken of the matter, however, is that it costs nothing for a master to afford these privileges—the work must at any rate be carried on, and is not retarded by being watched and learned by apprentices. Viewed from any point, the privileges of engineering establishments have to be considered as an element of value, to be bought at a price, just as a ton of iron or a certain amount of labour is; and in a commercial sense, as an exchangeable equivalent for labour, material, or money. In return a master receives the unskilled labour or service of the learner; this service is presumed to be given at a reduced rate, or sometimes without compensation, for the privileges of the works and the instruction received.
In forming an estimate of the value of his services, an apprentice sees what his hands have performed, compares it with what a skilled man will do, and estimates accordingly, assuming that his earnings are in proportion to what has been done; but this is a mistake, and a very different standard must be assumed to arrive at the true value of such unskilled labour.
Apprentice labour, as distinguished from skilled labour, has to be charged with the extra attention in management, the loss that is always occasioned by a forced classification of the work, the influence in lowering both the quality and the amount of work performed by skilled men, the risk of detention by failure or accident, and loss of material; besides, apprentices must be charged with the same, if not a greater expense than skilled workmen, for light, room, oil, tools, and office service. Attempts have been made in some of the best-regulated engineering establishments to fix some constant estimate upon apprentice labour, but, so far as known, without definite results in any case. If not combined with skilled labour, it would be comparatively easy to determine the value of apprentice labour; but when it comes up as an item in the aggregate of labour charged to a machine or some special work constructed, it is difficult, if not impossible, to separate skilled from unskilled service.
Another condition of apprenticeship that is equally as difficult to define as the commercial value of mechanical knowledge, or that of apprentice labour, is the extent and nature of the facilities that different establishments afford for learners.
In speaking of the mechanical knowledge to be gained, and of the privileges afforded for learners in engineering-works in a general way, it must, of course, be assumed that such works afford full facilities for learning some branch of work by the best practice and in the most thorough manner. Such establishments are, however, graded from the highest class, on the best branches of work, where a premium would be equitable, down to the lowest class, performing only inferior branches of work, where there can be little if any advantage gained by serving an apprenticeship.
Besides this want or difference of facilities which establishments may afford, there is the farther distinction to be made between an engineering establishment and one that is directed to the manufacture of staple articles. This distinction between engineering-works and manufacturing is quite plain to engineers themselves, but in many cases is not so to those who are to enter as apprentices, nor to their friends who advise them. In every case where engagements are made there should be the fullest possible investigation as to the character of the works, not only to protect the learner, but to guard regular engineering establishments in the advantages to be gained by apprentice labour. A machinist or a manufacturer who employs only the muscular strength and the ordinary faculties of workmen in his operations, can afford to pay an apprentice from the beginning a fair share of his earnings; but an engineering-work that projects original plans, generates designs, and assumes risks based upon skill and special knowledge, is very different from a manufactory. To manufacture is to carry on regular processes for converting material; such processes being constantly the same, or approximately so, and such as do not demand much mechanical knowledge on the part of workmen.
The name of having been an apprentice to a famous firm may sometimes have an influence in enabling an engineer to form advantageous commercial connections, but generally an apprenticeship is of value only as it has furnished substantial knowledge and skill; for every one must sooner or later come down to the solid basis of their actual abilities and acquirements. The engineering interest is by far too practical to recognise a shadow instead of true substance, and there is but little chance of deception in a calling which deals mainly with facts, figures, and positive demonstration.
It is best, when an apprentice thinks of entering an engineering establishment, to inquire of its character from disinterested persons who are qualified to judge of the facilities it affords. As a rule, every machine-shop proprietor imagines his own establishment to combine all the elements of an engineering business—and the fewer the facilities for learners, usually the more extravagant this estimate; so that opinions in the matter, to be relied upon, should come from disinterested sources.
In regard to premiums, it is a matter to be determined by the facilities that a work may afford for teaching apprentices. To include experience in all the departments of an engineering establishment, within a reasonable term, none but those of unusual ability can make their services of sufficient value to offset what they receive; and there is no doubt but that premium engagements, when the amount of the premium is based upon the facilities afforded for learning, are fair and equitable.
There is, however, this to be remembered, that the considerations which more especially balance premiums—such as a term at draughting, designing, and office service—may be mainly acquired by self-effort, while the practical knowledge of moulding, forging, and fitting cannot; and an apprentice who has good natural capacity, may, if industrious, by the aid of books and such opportunities as usually exist, qualify himself very well without including the premium departments in his course.
Finally, it must constantly be borne in mind that what will be learned is no less a question of faculties than effort, and that the means of succeeding are closed to none who at the beginning form proper plans, and follow them persistently.
(1.) Why cannot the conditions of apprentice engagements be determined by law?—(2.) In what manner does machine improvements affect the conditions of apprenticeship?—(3.) What are the considerations which pass from a master to an apprentice?—(4.) What from an apprentice to a master?—(5.) Why is a particular service of less value when performed by an apprentice than by a skilled workman?—(6.) In what manner can technical knowledge be made to balance or become capital?—(7.) Name two of the principal distinctions between technical knowledge and property as constituting capital.—(8.) What is the difference between what is called engineering and regular manufactures?
Mechanical engineering, like every other business pursuit, is directed to the accumulation of wealth; and as the attainment of any purpose is more surely achieved by keeping that purpose continually in view, there will be no harm, and perhaps considerable gain derived by an apprentice considering at the beginning the main object to which his efforts will be directed after learning his profession or trade. So far as an abstract principle of motives, the subject is of course unfit to consider in connection with engineering operations, or shop manipulation; but business objects have a practical application to be followed throughout the whole system of industrial pursuits, and are as proper to be considered in connection with machine-manufacturing as mechanical principles, or the functions and operation of machines.
The cost of production is an element that continually modifies or improves manufacturing processes, determines the success of every establishment, and must be considered continually in making drawings, patterns, forgings, and castings. Machines are constructed because of the difference between what they cost and what they sell for—between their manufacturing cost and market value when they are completed.
It seems hard to deprive engineering pursuits of the romance that is often attached to the business, and bring it down to a matter of commercial gain; but it is best to deal with facts, especially when such facts have an immediate bearing upon the general object in view. There is no intention in these remarks of disparaging the works of many noble men, who have given their means, their time, and sometimes their lives, to the advancement of the industrial arts, without hope or desire of any other reward than the satisfaction of having performed a duty; but we are dealing with facts, and no false colouring should prevent a learner from forming practical estimates of practical matters.
The following propositions will place this subject of aims and objects before the reader in the sense intended:—
First. The main object of mechanical engineering is commercial gain—the profits derived from planning and constructing machinery.
Second. The amount of gain so derived is as the difference between the cost of constructing machinery, and the market value of the machinery when completed.
Third. The difference between what it costs to plan and construct machinery and what it will sell for, is generally as the amount of engineering knowledge and skill brought to bear in the processes of production.
This last sentence brings the matter into a tangible form, and indicates what the subject of gain should have to do with what an apprentice learns of machine construction. Success in an engineering enterprise may be temporarily achieved by illegitimate means—such as misrepresentation of the capacity and quality of what is produced, the use of cheap or improper material, or by copying the plans of others to avoid the expense of engineering service—but in the end the permanent success of an engineering business must rest upon the knowledge and skill that is connected with it.
By examining into the facts, an apprentice will find that all truly successful establishments have been founded and built upon the mechanical abilities of some person or persons whose skill formed a base upon which the business was reared, and that true skill is the element which must in the end lead to permanent success. The material and the labour which make up the first cost of machines are, taking an average of various classes, nearly equally divided; labour being in excess for the finer class of machinery, and the material in excess for the coarser kinds of work. The material is presumed to be purchased at the same rates by those of inferior skill as by those that are well skilled, so that the difference in the first, or manufacturing cost of machinery, is determined mainly by skill.
Skill, in the sense employed here, consists not only in preparing plans and in various processes for converting and shaping material, but also in the general conduct of an establishment, including estimates, records, system, and so on, which will be noticed in their regular order. The amount of labour involved, and consequently the first cost of machinery, is in a large degree as the number of mechanical processes required, and the time consumed in each operation; to reduce the number of these processes or operations, shorten the time in which they may be performed, and improve the quality of what is produced, is the business of the mechanical engineer. A careful study of shop operations or processes, including designing, draughting, moulding, forging, and fitting, is the secret of success in engineering practice, or in the management of manufactures. The advantages of an economical design, and the most carefully-prepared drawings, are easily neutralised and lost by careless or improper manipulation in the workshop; an incompetent manager may waste ten pounds in shop processes, while the commercial department of a work saves one pound by careful buying and selling.
This importance of shop processes in machine construction is generally realised by proprietors, but not thoroughly understood in all of its bearings; an apprentice may notice the continual effort that is made to augment the production of engineering-works, which is the same thing as shortening the processes.
A machine may be mechanically correct, arranged with symmetry, true proportions, and proper movements; but if such a machine has not commercial value, and is not applicable to a useful purpose, it is as much a failure as though it were mechanically inoperative. In fact, this consideration of cost and commercial value must be continually present; and a mechanical education that has not furnished a true understanding of the relations between commercial cost and mechanical excellence will fall short of achieving the objects for which such an education is undertaken. By reasoning from such premises as have been laid down, an apprentice may form true standards by which to judge of plans and processes that he is brought in contact with, and the objects for which they are conducted.
(1.) To what general object are all pursuits directed?—(2.) What besides wealth may be objects in the practice of engineering pursuits?—(3.) Name some of the most common among the causes which reduce the cost of production.—(4.) Name five of the main elements which go to make up the cost of engineering products.—(5.) Why is commercial success generally a true test of the skill connected with engineering-works?
Machines do not create or consume, but only transmit and apply power; and it is only by conceiving of power as a constant element, independent of every kind of machinery, that the learner can reach a true understanding of the nature of machines. When once there is in the mind a fixed conception of power, dissociated from every kind of mechanism, there is laid, so to speak, a solid foundation on which an understanding of machines may be built up.
To believe a fact is not to learn it, in the sense that these terms may be applied to mechanical knowledge; to believe a proposition is not to have a conviction of its truth; and what is meant by learning mechanical principles is, as remarked in a previous place, to have them so fixed in the mind that they will involuntarily arise to qualify everything met with that involves mechanical movement. For this reason it has been urged that learners should begin by first acquiring a clear and fixed conception of power, and next of the nature and classification of machines, for without the first he cannot reach the second.
Machines may be defined in general terms as agents for converting, transmitting, and applying power, or motion and force, which constitute power. By machinery the natural forces are utilised, and directed to the performance of operations where human strength is insufficient, when natural force is cheaper, and when the rate of movement exceeds what the hands can perform. The term "agent" applied to machines conveys a true idea of their nature and functions.
Machinery can be divided into four classes, each constituting a division that is very clearly defined by functions performed, as follows:—
First. Motive machinery for utilising or converting the natural forces.
Second. Machinery for transmitting and distributing power.
Third. Machinery for applying power.
Fourth. Machinery of transportation.
Or, more briefly stated—
Motive machinery.
Machinery of transmission.
Machinery of application.
Machinery of transportation.
These divisions of machinery will next be treated of separately, with a view of making the classification more clear, and to explain the principles of operation in each division. This dissertation will form a kind of base upon which the practical part of the treatise will in a measure rest. It is trusted that the reader will carefully consider each proposition that is laid down, and on his own behalf pursue the subjects farther than the limits here permit.
(1.) To what three general objects are machines directed?—(2.) How are machines distinguished from other works or structures?—(3.) Into what four classes can machinery be divided?—(4.) Name one principal type in each of these four divisions.
In this class belong—
Steam-engines.
Caloric or air engines.
Water-wheels or water-engines.
Wind-wheels or pneumatic engines.
These four types comprehend the motive-power in general use at the present day. In considering different engines for motive-power in a way to best comprehend their nature, the first view to be taken is that they are all directed to the same end, and all deal with the same power; and in this way avoid, if possible, the impression of there being different kinds of power, as the terms water-power, steam-power, and so on, seem to imply. We speak of steam-power, water-power, or wind-power; but power is the same from whatever source derived, and these distinctions merely indicate different natural sources from which power is derived, or the different means employed to utilise and apply it.
Primarily, power is a product of heat; and wherever force and motion exist, they can be traced to heat as the generating element: whether the medium through which the power is obtained be by the expansion of water or gases, the gravity of water, or the force of wind, heat will always be found as the prime source. So also will the phenomenon of expansion be found a constant principle of developing power, as will again be pointed out. As steam-engines constitute a large share of the machinery commonly met with, and as a class of machinery naturally engrosses attention in proportion, the study of mechanics generally begins with steam-engines, or steam machinery, as it may be called.
The subject of steam-power, aside from its mechanical consideration, is one that may afford many useful lessons, by tracing its history and influence, not only upon mechanical industry, but upon human interests generally. This subject is often treated of, and both its interest and importance conceded; but no one has, so far as I know, from statistical and other sources, ventured to estimate in a methodical way the changes that can be traced directly and indirectly to steam-power.
The steam-engine is the most important, and in England and America best known among motive agents. The importance of steam contrasted with other sources of motive-power is due not so much to a diminished cost of power obtained in this way, but for the reason that the amount of power produced can be determined at will, and in most cases without reference to local conditions; the machinery can with fuel and water be transported from place to place, as in the case of locomotives which not only supply power for their own transit, but move besides vast loads of merchandise, or travel.
For manufacturing processes, one importance of steam-power rests in the fact that such power can be taken to the material; and beside other advantages gained thereby, is the difference in the expense of transporting manufactured products and the raw material. In the case of iron manufacture, for example, it would cost ten times as much to transport the ore and the fuel used in smelting as it does to transport the manufactured iron; steam-power saves this difference, and without such power our present iron traffic would be impossible. In a great many manufacturing processes steam is required for heating, bleaching, boiling, and so on; besides, steam is now to a large extent employed for warming buildings, so that even when water or other power is employed, in most cases steam-generating apparatus has to be set up in addition. In many cases waste steam or waste heat from a steam-engine can be employed for the purposes named, saving most of the expense that must be incurred if special apparatus is employed.
Other reasons for the extended and general use of steam as a power, besides those already named, are to be found in the fact that no other available element or substance can be expanded to a given degree at so small a cost as water; and that its temperature will not rise to a point injurious to machinery, and, further, in the very important property of lubrication which steam possesses, protecting the frictional surfaces of pistons and valves, which it is impossible to keep oiled because of their inaccessibility or temperature.
The steam-engine, in the sense in which the term is employed, means not only steam-using machinery, but steam-generating machinery or plant; it includes the engine proper, with the boiler, mechanism for feeding water to the boiler, machinery for governing speed, indicators, and other details.
An apprentice must guard against the too common impression that the engine, cylinder, piston, valves, and so on, are the main parts of steam machinery, and that the boiler and furnace are only auxiliaries. The boiler is, in fact, the base of the whole, that part where the power is generated, the engine being merely an agent for transmitting power from the boiler to work that is performed. This proposition would, of course, be reached by any one in reasoning about the matter and following it to a conclusion, but the fact should be fixed in the mind at the beginning.
When we look at a steam-engine there are certain impressions conveyed to the mind, and by these impressions we are governed in a train of reflection that follows. We may conceive of a cylinder and its details as a complete machine with independent functions, or we can conceive of it as a mechanical device for transmitting the force generated by a boiler, and this conception might be independent of, or even contrary to, specific knowledge that we at the same time possessed; hence the importance of starting with a correct idea of the boiler being, as we may say, the base of steam machinery.
As reading books of fiction sometimes expands the mind and enables it to grasp great practical truths, so may a study of abstract principles often enable us to comprehend the simplest forms of mechanism. Even Humboldt and Agassiz, it is said, resorted sometimes to imaginative speculations as a means of enabling them to grasp new truths.
In no other branch of machinery has so much research and experiment been made during eighty years past as in steam machinery, and, strange to say, the greater part of this research has been directed to the details of engines; yet there has been no improvement made during the time which has effected any considerable saving of heat or expense. The steam-engines of fifty years ago, considered as steam-using machines, utilised nearly the same proportion of the energy or power developed by the boiler as the most improved engines of modern construction—a fact that in itself indicates that an engine is not the vital part of steam machinery. There is not the least doubt that if the efforts to improve steam-engines had been mainly directed to economising heat and increasing the evaporative power of boilers, much more would have been accomplished with the same amount of research. This remark, however, does not apply to the present day, when the principles of steam-power are so well understood, and when heat is recognised as the proper element to deal with in attempts to diminish the expense of power. There is, of course, various degrees of economy in steam-using as well as in steam-generating machinery; but so long as the best steam machinery does not utilise but one-tenth or one-fifteenth part of the heat represented in the fuel burned, there need be no question as to the point where improvements in such machinery should be mainly directed.
The principle upon which steam-engines operate may be briefly explained as follows:—
A cubic inch of water, by taking up a given amount of heat, is expanded to more than five hundred cubic inches of steam, at a pressure of forty-five pounds to the square inch. This extraordinary expansion, if performed in a close vessel, would exert a power five hundred times as great as would be required to force the same quantity of water into the vessel against this expansive pressure; in other words, the volume of the water when put into the vessel would be but one five-hundredth part of its volume when it is allowed to escape, and this expansion, when confined in a steam-boiler, exerts the force that is called steam-power. This force or power is, through the means of the engine and its details, communicated and applied to different kinds of work where force and movement are required. The water employed to generate steam, like the engine and the boiler, is merely an agent through which the energy of heat is applied.
This, again, reaches the proposition that power is heat, and heat is power, the two being convertible, and, according to modern science, indestructible; so that power, when used, must give off its mechanical equivalent of heat, or heat, when utilised, develop its equivalent in power. If the whole amount of heat represented in the fuel used by a steam-engine could be applied, the effect would be, as before stated, from ten to fifteen times as great as it is in actual practice, from which it must be inferred that a steam-engine is a very imperfect machine for utilising heat. This great loss arises from various causes, among which is that the heat cannot be directly nor fully communicated to the water. To store up and retain the water after it is expanded into steam, a strong vessel, called a boiler, is required, and all the heat that is imparted to the water has to pass through the plates of this boiler, which stand as a wall between the heat and its work.
To summarise, we have the following propositions relating to steam machinery:—
1. The steam-engine is an agent for utilising the power of heat and applying it to useful purposes.
2. The power of a steam-engine is derived by expanding water in a confining vessel, and employing the force exerted by pressure thus obtained.
3. The power developed is as the difference of volume between the feed-water forced into the boiler, and the volume of the steam that is drawn from the boiler, or as the amount of heat taken up by the water.
4. The heat that may be utilised is what will pass through the plates of the boiler, and be taken up by the water, and is but a small share of what the fuel produces.
5. The boiler is the main part, where power is generated, and the engine is but an agent for transmitting this power to the work performed.
6. The loss of power in a steam-engine arises from the heat carried off in the exhaust steam, loss by radiation, and the friction of the moving parts.
7. By condensing the steam before it leaves the engine, so that the steam is returned to the air in the form of water, and of the same volume as when it entered the boiler, there is a gain effected by avoiding atmospheric pressure, varying according to the perfection of the arrangements employed.
Engines operated by means of hot air, called caloric engines, and engines operated by gas, or explosive substances, all act substantially upon the same general principles as steam-engines; the greatest distinction being between those engines wherein the generation of heat is by the combustion of fuel, and those wherein heat and expansion are produced by chemical action. With the exception of a limited number of caloric or air engines, steam machinery comprises nearly all expansive engines that are employed at this day for motive-power; and it may be safely assumed that a person who has mastered the general principles of steam-engines will find no trouble in analysing and understanding any machinery acting from expansion due to heat, whether air, gas, or explosive agents be employed.
This method of treating the subject of motive-engines will no doubt be presenting it in a new way, but it is merely beginning at an unusual place. A learner who commences with first principles, instead of pistons, valves, connections, and bearings, will find in the end that he has not only adopted the best course, but the shortest one to understand steam and other expansive engines.
(1.) What is principal among the details of steam machinery?—(2.) What has been the most important improvement recently made in steam machinery?—(3.) What has been the result of expansive engines generally stated?—(4.) Why has water proved the most successful among various expansive substances employed to develop power?—(5.) Why does a condensing engine develop more power than a non-condensing one?—(6.) How far back from its development into power can heat be traced as an element in nature?—(7.) Has the property of combustion a common source in all substances?
Water-wheels, next to steam-engines, are the most common motive agents. For centuries water-wheels remained without much improvement or change down to the period of turbine wheels, when it was discovered that instead of being a very simple matter, the science of hydraulics and water-wheels involved some very intricate conditions, giving rise to many problems of scientific interest, that in the end have produced the class known as turbine wheels.
A modern turbine water-wheel, one of the best construction, operating under favourable conditions, gives a percentage of the power of the water which, after deducting the friction of the wheel, almost reaches the theoretical coefficient or equals the gravity of the water; it may therefore be assumed that there will in the future be but little improvement made in such water-wheels except in the way of simplifying and cheapening their construction. There is, in fact, no other class of machines which seem to have reached the same state of improvement as water-wheels, nor any other class of machinery that is constructed with as much uniformity of design and arrangement, in different countries, and by different makers.
Water-wheels, or water-power, as a mechanical subject, is apparently quite disconnected with shop manipulation, but will serve as an example for conveying general ideas of force and motion, and, on these grounds, will warrant a more extended notice than the seeming connection with the general subject calls for.
In the remarks upon steam-engines it was explained that power is derived from heat, and that the water and the engine were both to be regarded as agents through which power was applied, and further, that power is always a product of heat. There is, perhaps, no problem in the whole range of mechanics more interesting than to trace the application of this principle in machinery; one that is not only interesting but instructive, and may suggest to the mind of an apprentice a course of investigation that will apply to many other matters connected with power and mechanics.
Power derived from water by means of wheels is due to the gravity of the water in descending from a higher to a lower level; but the question arises, What has heat to do with this? If heat is the source of power, and power a product of heat, there must be a connection somewhere between heat and the descent of the water. Water, in descending from one level to another, can give out no more power than was consumed in raising it to the higher level, and this power employed to raise the water is found to be heat. Water is evaporated by heat of the sun, expanded until it is lighter than the atmosphere, rises through the air, and by condensation falls in the form of rain over the earth's surface; then drains into the ocean through streams and rivers, to again resume its round by another course of evaporation, giving out in its descent power that we turn to useful account by means of water-wheels. This principle of evaporation is continually going on; the fall of rain is likewise quite constant, so that streams are maintained within a sufficient regularity to be available for operating machinery.
The analogy between steam-power and water-power is therefore quite complete. Water is in both cases the medium through which power is obtained; evaporation is also the leading principle in both, the main difference being that in the case of steam-power the force employed is directly from the expansion of water by heat, and in water-power the force is an indirect result of expansion of water by heat.
Every one remembers the classification of water-wheels met with in the older school-books on natural philosophy, where we are informed that there are three kinds of wheels, as there were "three kinds of levers"—namely, overshot, undershot, and breast wheels—with a brief notice of Barker's mill, which ran apparently without any sufficient cause for doing so. Without finding fault with the plan of describing water-power commonly adopted in elementary books, farther than to say that some explanation of the principles by which power is derived from the water would have been more useful, I will venture upon a different classification of water-wheels, more in accord with modern practice, but without reference to the special mechanism of the different wheels, except when unavoidable. Water-wheels can be divided into four general types.
First. Gravity wheels, acting directly from the weight of the water which is loaded upon a wheel revolving in a vertical plane, the weight resting upon the descending side until the water has reached the lowest point, where it is discharged.
Second. Impact wheels, driven by the force of spouting water that expends its percussive force or momentum against the vanes tangental to the course of rotation, and at a right angle to the face of the vanes or floats.
Third. Reaction wheels, that are "enclosed," as it is termed, and filled with water, which is allowed to escape under pressure through tangental orifices, the propelling force being derived from the unbalanced pressure within the wheel, or from the reaction due to the weight and force of the water thrown off from the periphery.
Fourth. Pressure wheels, acting in every respect upon the principle of a rotary steam-engine, except in the differences that arise from operating with an elastic and a non-elastic fluid; the pressure of the water resting continually against the vanes and "abutment," without means of escape except by the rotation of the wheel.
To this classification may be added combination wheels, acting partly by the gravity and partly by the percussion force of the water, by impact combined with reaction, or by impact and maintained pressure.
Gravity, or "overshot" wheels, as they are called, for some reasons will seem to be the most effective, and capable of utilising the whole effect due to the gravity of the water; but in practice this is not the case, and it is only under peculiar conditions that wheels of this class are preferable to turbine wheels, and in no case will they give out a greater per cent. of power than turbine wheels of the best class. The reasons for this will be apparent by examining the conditions of their operation.
A gravity wheel must have a diameter equal to the fall of water, or, to use the technical name, the height of the head. The speed at the periphery of the wheel cannot well exceed sixteen feet per second without losing a part of the effect by the wheel anticipating or overrunning the water. This, from the large diameter of the wheels, produces a very slow axial speed, and a train of multiplying gearing becomes necessary in order to reach the speed required in most operations where power is applied. This train of gearing, besides being liable to wear and accident, and costing usually a large amount as an investment, consumes a considerable part of the power by frictional resistance, especially when such gearing consists of tooth wheels. Gravity wheels, from their large size and their necessarily exposed situation, are subject to be frozen up in cold climates; and as the parts are liable to be first wet and then dry, or warm and cold by exposure to the air and the water alternately, the tendency to corrosion if constructed of iron, or to decay if of wood, is much greater than in submerged wheels. Gravity wheels, to realise the highest measure of effect from the water, require a diameter so great that they must drag in the water at the bottom or delivering side, and are for this reason especially affected by back-water, to which all wheels are more or less liable from the reflux of tides or by freshets. These disadvantages are among the most notable pertaining to gravity wheels, and have, with other reasons—such as the inconvenience of construction, greater cost, and so on—driven such wheels out of use by the force of circumstances, rather than by actual tests or theoretical deductions.
Impact wheels, or those driven by the percussive force of water, including the class termed turbine water-wheels, are at this time generally employed for heads of all heights.
The general theory of their action may be explained in the following propositions:—
1. The spouting force of water is theoretically equal to its gravity.
2. The percussive force of spouting water can be fully utilised if its motion is altogether arrested by the vanes of a wheel.
3. The force of the water is greatest by its striking against planes at right angles to its course.
4. Any force resulting from water rebounding from the vanes parallel to their face, or at any angle not reverse to the motion of the wheel, is lost.
5. This rebounding action becomes less as the columns of water projected upon the wheel are increased in number and diminished in size.
6. To meet the conditions of rotation in the wheel, and to facilitate the escape of the water without dragging, after it has expended its force upon the vanes, the reversed curves of the turbine is the best-known arrangement.
It is, of course, very difficult to deal with so complex a subject as the present one with words alone, and the reader is recommended to examine drawings, or, what is better, water-wheels themselves, keeping the above propositions in view.
Modern turbine wheels have been the subject of the most careful investigation by able engineers, and there is no lack of mathematical data to be referred to and studied after the general principles are understood. The subject, as said, is one of great complicity if followed to detail, and perhaps less useful to a mechanical engineer who does not intend to confine his practice to water-wheels, than other subjects that may be studied with greater advantage. The subject of water-wheels may, indeed, be called an exhausted one that can promise but little return for labour spent upon it—with a view to improvements, at least. The efforts of the ablest hydraulic engineers have not added much to the percentage of useful effect realised by turbine wheels during many years past.
Reaction wheels are employed to a limited extent only, and will soon, no doubt, be extinct as a class of water-wheels. In speaking of reaction wheels, I will select what is called Barker's mill for an example, because of the familiarity with which it is known, although its construction is greatly at variance with modern reaction wheels.
There is a problem as to the principle of action in a Barker wheel, which although it may be very clear in a scientific sense, remains a puzzle to the minds of many who are well versed in mechanics, some contending that the power is directly from pressure, others that it is from the dynamic effect due to reaction. It is one of the problems so difficult to determine by ordinary standards, that it serves as a matter of endless debate between those who hold different views; and considering the advantage usually derived from such controversies, perhaps the best manner of disposing of the problem here is to state the two sides as clearly as possible, and leave the reader to determine for himself which he thinks right.
Presuming the vertical shaft and the horizontal arms of a Barker wheel to be filled with water under a head of sixteen feet, there would be a pressure of about seven pounds upon each superficial inch of surface within the cross arm, exerting an equal force in every direction. By opening an orifice at the sides of these arms equal to one inch of area, the pressure would at that point be relieved by the escape of the water, and the internal pressure be unbalanced to that extent. In other words, opposite this orifice, and on the other side of the arm, there would be a force of seven pounds, which being unbalanced, acts as a propelling power to drive the wheel.
This is one theory of the principle upon which the Barker wheel operates, which has been laid down in Vogdes' "Mensuration," and perhaps elsewhere. The other theory alluded to is that, direct action and reaction being equal, ponderable matter discharged tangentally from the periphery of a wheel must create a reactive force equal to the direct force with which the weight is thrown off. To state it more plainly, the spouting water that issues from the arm of a Barker wheel must react in the opposite course in proportion to its weight.
The two propositions may be consistent with each other or even identical, but there still remains an apparent difference.
The latter seems a plausible theory, and perhaps a correct one; but there are two facts in connection with the operation of reaction water-wheels which seem to controvert the latter and favour the first theory, namely, that reaction wheels in actual practice seldom utilise more than forty per cent. of useful effect from the water, and that their speed may exceed the initial velocity of the water. With this the subject is left as one for argument or investigation on the part of the reader.
Pressure wheels, like gravity wheels, should, from theoretical inference, be expected to give a high per cent. of power. The water resting with the whole of its weight against the vanes or abutments, and without chance of escape except by turning the wheel, seems to meet the conditions of realising the whole effect due to the gravity of the water, and such wheels would no doubt be economical if they had not to contend with certain mechanical difficulties that render them impracticable in most cases.
A pressure wheel, like a steam-engine, must include running contact between water-tight surfaces, and like a rotary steam-engine, this contact is between surfaces which move at different rates of speed in the same joint, so that the wear is unequal, and increases as the speed or the distance from the axis. When it is considered that the most careful workmanship has never produced rotary engines that would surmount these difficulties in working steam, it can hardly be expected they can be overcome in using water, which is not only liable to be filled with grit and sediment, but lacks the peculiar lubricating properties of steam. A rotary steam-engine is in effect the same as a pressure water-wheel, and the apprentice in studying one will fully understand the principles of the other.
(1.) What analogy may be found between steam and water power?—(2.) What is the derivation of the name turbine?—(3.) To what class of water-wheels is this name applicable?—(4.) How may water-wheels be classified?—(5.) Upon what principle does a reaction water-wheel operate?—(6.) Can ponderable weight and pressure be independently considered in the case?—(7.) Why cannot radial running joints be maintained in machines?—(8.) Describe the mechanism in common use for sustaining the weight of turbine wheels, and the thrust of propeller shafts.
Wind-power, aside from the objections of uncertainty and irregularity, is the cheapest kind of motive-power. Steam machinery, besides costing a large sum as an investment, is continually deteriorating in value, consumes fuel, and requires continual skilled attention. Water-power also requires a large investment, greater in many cases than steam-power, and in many places the plant is in danger of destruction by freshets. Wind-power is less expensive in every way, but is unreliable for constancy except in certain localities, and these, as it happens, are for the most part distant from other elements of manufacturing industry. The operation of wind-wheels is so simple and so generally understood that no reference to mechanism need be made here. The force of the wind, moving in right lines, is easily applied to producing rotary motion, the difference from water-power being mainly in the comparative weakness of wind currents and the greater area required in the vanes upon which the wind acts. Turbine wind-wheels have been constructed on very much the same plan as turbine water-wheels. In speaking of wind-power, the propositions about heat must not be forgotten. It has been explained how heat is almost directly utilised by the steam-engine, and how the effect of heat is utilised by water-wheels in a less direct manner, and the same connection will be found between heat and wind-wheels or wind-power. Currents of air are due to changes of temperature, and the connection between the heat that produces such air currents and their application as power is no more intricate than in the case of water-power.
(1.) What is the difference in general between wind and water wheels?—(2.) Can the course of wind, like that of water, be diverted and applied at pleasure?—(3.) On what principle does wind act against the vanes of a wheel?—(4.) How may an analogy between wind-power and heat be traced?